Formation evaluation method and apparatus



Feb. 28, 1967 M. P. LEBOURG 3,306,102

FORMATION EVALUATION METHOD AND APPARATUS Filed Dec. 4, 1965 5Sheets-Sheet l a e a Maw/me f? Zeboory INVENTOR.

Feb. 28, 1967 LEBOURG 3,306,102

FORMATION EVALUATION METHOD AND APPARATUS Filed Dec. 4, 1965 5Sheets-Sheet 2 fiA AIM 6 MOO/V66 P. Zebu/r9 INVENTOR.

ATTOR/Vf Feb. 28, 1967 M. P. LEBOURG FORMATION EVALUATION METHOD ANDAPPARATUS Filed Dec. 4, 1963 5 Sheets-Sheet 3 Maw/me P. Labour INVENTOR.

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ATTOF/Vfy Feb. 28, 1967 LEBOURG 3,306,102

FORMATION EVALUATION METHOD AND APPARATUS Filed Dec. 4, 1963 5Sheets-Sheet 4 Maw/me P. Leourg INVENTOR.

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FORMATION EVALUATION METHOD AND APPARATUS Filed Dec. 4, 1965 5Sheets-Sheet 5 INVEN Q? /)/)lP/)l bl bib/bl), 1! a x Q IX Illll m .1.J'K HPIJW... t l .AZ A B 5 n w M Moor/re P labour United States Patent@flice 33%,162 Pei-tented Feb. 28, 19%? 3,306,102 FURMATION EVALUATIONMETHOD AND APPARATUS Maurice P. Lebourg, Houston, Tex., assignor, bymesne assignments, to Schlumbergcr Technology Corporation, Houston,Tex., a corporation of Texas Filed Dec. 4, 1963, Ser. No. 327,947 34Claims. (Cl. 73155) This invention relates, in general, to novel methodsand apparatus for investigating earth formations traversed by a wellbore, and more particularly, to methods and apparatus for investigatingearth formations and obtaining characteristic data pertinent to the typeof subterranean earth formations and the fluids present within suchformations.

While drilling a well, a viscous drilling fluid (known as mud) iscommonly circulated down the drill pipe and back up the annular spacebetween the drill pipe and the well bore. This mud, which is typically ablended composition of high-viscosity organic and inorganic materials,contains a large percentage of suspended solids. The circulated mudremoves the earth materials as they are cut-away by the drill bit aswell as maintains a hydrostatic pressure within the borehole greaterthan the natural pressure of fluids contained within any fluid-bearingpermeable formations traversed by the borehole.

As is well-known in the art, the higher hydrostatic pressure imposed onthe formations by the drilling mud unavoidably forces some of the liquidphase of the drilling mud into any permeable formation strata exposed tothe well bore. The solid particles carried in suspension by this liquidare filtered out onto the exposed faces of permeable formations as theliquid or filtrate invades the formations. These solid particlescontinue to build up to form a mudcake usually characterized by a verylow permeability. In the formation of this mudcake, the filtratedisplaces the formation fluids radially away from the borehole.

After a well bore has been drilled, or during the drilling of a well ifthe drilling string is removed, it is customary to conduct one or morewell-logging operations to determine the nature of the various formationfluids and strata traversed by the well bore. These operations typicallyinclude the lowering of electrical logging, radioactivity logging orsonic logging devices into the well bore, either separately or incombination, by means of an armored electrical cable. Data obtained fromsuch logging operations is subsequently studied and predictions madetherefrom as to the geological nature of the various strata traversed bythe well bore, their porosity and permeability, and the type andquantity of fluids contained therein. Experience will then dictate whichparticular strata are most likely to contain producible hydrocarbons. Itis recognized by those skilled in the art that some formation parametersobtainable by logging operations are altered or aifected by the presenceof a mudcake and by the extent of filtrate invasion. Such measurementsas formation resistivity, for example, will be appreciably influenced bythe fact that the resistivity of the filtrate will generally bedifferent than the resistivity of the natural or connate formationfluids displaced by the invasion of the filtrate. Furthermore, it isrealized that the resistivity of the mudcake itself will be included inthe total resistivity measured. Corrections can be made, of course, todetermine the resistivity of the unaltered formation with only itsconnate fluids, but such corrections require making several measurementswith the same and different instruments as well as several passages orround trips of the instruments into and out of the well bore.

Other types of measurements may be made which are also affected by theextent of filtrate invasion. For example, as shown and described inPatent No. 3,108,188, the presence or absence of saline connateformation water in a particular permeable formation can be predicted. Itwill be appreciated that such measurements would be affected by invasionof a relatively fresh mud filtrate.

Often it is desirable to supplement or confirm the results obtained fromanalysis of such formation-logging data by conducting a drillstem testwhich heretofore has been performed wholly independently of the loggingoperations. In general, the particular formation zones which warranttesting can be selected by analysis of the logging data. From suchdrillstem tests, it is then possible to predict the potential productionpossibilities of those formations tested.

Drillstem tests are conducted by lowering into the well a drillstemtester depending from a string of pipe. The tester includes a suitablepacker arrangement adapted for sealing off the annular space between thedrillstem tester and the borehole wall to isolate a selected zone fromthe hydrostatic head of the drilling mud in the well bore above thepacker before conducting the drillstem test. After the packer is set, avalve in the drillstem tester is then opened by manipulation of thestring of pipe to permit fluids contained within the formations beinginvestigated to flow outwardly therefrom, into the drillstem tester, andon upwardly through the string of pipe which is at a lower pressure thanthe formation fluids. Measurements of formation pressures are usuallymade during the drillstem-testing operations by a self-containeddownhole instrument. In addition, samples of fluids which flow withinthe string of pipe are often obtained and analyzed.

The flushin action of formation fluids flowing into the well during adrillstem test is expected to displace most, if not all, of the mudcaked on the exposed borehole surfaces of the fluid-bearing permeableformations along the isolated section as well as to force out the mudfiltrate which has invaded these formations. After such flushing, onemay expect to recover the connate fluids naturally contained within thepermeable formations. Following a drillstem test, conditions within theWell again stabilize as the drilling mud filtrate reinvades thepermeable formations with the attending redepositing of the mudcake. Thelength of time required for this reinvasion and recaking process isvariable since this time interval will be dependent upon many factorssuch as porosity, permeability, formation pressures, types of drillingmuds, etc. Those skilled in the art do recognize, however, that thisre-establishment of conditions or restabilization generally takes placein a relatively short time.

The time required for restabilization is generally too short, however,to obtain logging data of the formations in their unaltered condition byconventional methods which would necessitate first removing the drillstring a section at a time to retrieve the drillstem tester and thenrepositioning a formation-logging instrument into the well bore, all ofwhich would consume an appreciable amount of time. Furthermore, even ifsuch logs were made, there would be no way to accurately predict whatcompensating corrections would be required, not knowing the extent offiltrate reinvasion during the time required to remove the drillstemtester and reposition the logging instruments. It will be appreciated,moreover, that it is economically desirable to reduce the amount of timethat drilling or other operations on a well are suspended whileconducting such logging and testing operations.

It is, therefore, an object of the present invention to provide new andimproved methods for investigating the natural characteristics ofpermeable earth formations and for assisting in the completion of aWell.

It is also an object of the present invention to provide new andimproved systems for determining the natural characteristics of earthformations which require only a single round trip into and out of thewell bore.

A further object of the present invention is to provide new and improvedsystems for obtaining formation data which is useful in predicting theproduction potential of a particular well and for assisting in thecompletion of that well.

Another object of the present invention is to provide new and improvedsystems for obtaining data which is indicative of characteristics ofpermeable formations without the influence of drilling mud or mudfiltrate.

Still another object of the present invention is to provide new andimproved systems for determining the effects of filtrate invasion aswell as the flow characteristics of a well.

It is yet a further object of the invention to flow fluids from theearth formations and, before any substantial mudcake and filtrateinvasion can reoccur, perform a series of logging operations to obtainformation data relative to the natural formation fluids containedtherein.

The novel methods of the present invention are practiced by firstreducing the well bore pressure opposite a particular formation intervalto be investigated to allow the fluids contained in the permeableformations in that interval to flow into the well bore. This How ismaintained until the connate formation fiuids have substantiallydisplaced the drilling mud filtrate which had previously invaded theformations and washed away the accumulated mudcake along the wall of thewell bore. Then, before any substantial reinvasion of filtrate canoccur, a series of measurements are taken along the formation intervalof those formation properties or characteristics which are altered oraffected by the invasion of mud filtrate within the permeableformations.

The particular interval tested can be along any section or all of thewell bore if so desired. Additionally, a first series of suchmeasurements may be taken before the flowing step as well as taking asecond series afterward if it is desired to obtain correlative datawhich will be indicative of the effects of filtrate invasion and theflow characteristics of the formations tested. Where it is preferred,additional measurements may also be made of formation properties notaffected by filtrate invasion simultaneously with the first and secondseries of measurements for aid in correlating the first and secondseries and for purposes of reference in subsequent completionoperations.

A preferred form of apparatus to be used in practicing the novel methoddisclosed herein is made by combining flow-testing apparatus withformation-logging apparatus so that the combined apparatus can becontrolled from the surface while suspended in a well bore on a stringof pipe for containing the fluids produced from the formations. The flowtester preferably includes a packer means to isolate a formationinterval to be tested and a selectively-operable valve to control flowbetween the tested interval and the string of pipe. This type of flowapparatus can be found in a conventional drillstem tester. Theformation-log ing apparatus need have only a single instrument, forexample, a chloride-ion measuring device or a formation-resistivitymeasuring device, but preferably also includes a gamma-ray radiationdetection device. Self-contained recording instruments are provided forrecording of data.

The novel features of the present invention are set forth withparticularity in the appended claims. The present invention, both as toits organization and manner of operation together with further objectsand advantages thereof, may best be understood by way of illustrationand example of certain embodiments when taken in conjunction with theaccompanying drawings, in which:

FIG. 1A illustrates a testing apparatus being lowered into a well;

FIG. 1B illustrates a testing apparatus logging a well bore in which amudcake has formed and mud filtrate has invaded the permeableformations;

FIG. 1C illustrates a testing apparatus during a flow testing operation;

FIG. 1D illustrates a testing apparatus being used to obtain a logbefore mudcake has reformed and filtrate has reinvaded the permeableformations;

FIG. 1E illustrates a testing apparatus from a well;

FIG. 2A shows typical-formation logs or films strips representative ofmeasurements recorded in the logging step illustrated in FIG. 1B;

FIG. 2B shows typical formation logs or film strips representative ofmeasurements recorded in the logging step illustrated in FIG. 1D;

FIG. 2C shows the typical formation logs or film strips of FIGS. 2A and23 combined with one another to illustrate the difierences between logsobtained prior to the flow testing and after the flow testing;

FIG. 3 is a longitudinal view, partly in section, of an embodiment oftesting apparatus of the present invention, the parts being shown in therelative positions occupied while the testing apparatus is within thewell bore;

FIG. 4A shows an embodiment of a switching assembly used for controllingthe apparatus shown in FIG. 7;

FIG. 4B shows an alternative embodiment of a switching assembly;

FIG. 5 shows a relay circuit which may be used in controlling theelectrical circuitry;

FIG. 6A shows typical formation logs or film such as those of FIG. 2Awith an additinal record;

FIG. 6B shows typical formation logs or film such as those of FIG. 2Bwith an additional record;

FIG. 60 shows the typical formation logs or film strips of FIGS. 6A and6B combined with one another to illustrate the differences between logsobtained prior to the flow testing and after the flow testing;

FIG. 7 is a longitudinal view, partly in section of another embodimentof testing apparatus of the present invention which is similar to theembodiment shown in FIG. 3 but with the addition of a calipering loggingdevice; and

FIG. 8 is a longitudinal view of a perforating tool being used topractice a method of the invention.

In practicing the method of the present invention, a testing apparatus Tis lowered into a well bore 10 as shown in FIG. 1A. The apparatuspreferably includes a flow tester F, a packer P, a perforated pipe R anda formationlogging instrument I. The section of earth formations to beinvestigated as shown in FIGS. lA-lE (identified only in FIG. 1E) mayinclude permeable oil-bearing earth formations B and permeablewater-bearing formations C separated by impermeable shale formations A.The exposed faces of permeable formations B and C are coated with amudcake 11 and mud filtrate has invaded these zones to a depth indicatedat 12 (FIG. 1A). The predetermined zone to be investigated is assumed toinclude these designated formations.

As seen in FIGS. 1A and 1B, the testing apparatus is first lowered tothe bottom of the well bore (as shown by the dotted lines in FIG. 1B)and then raised to a level where the packer P is at least above theupppermost permeable earth formation B. During this traverse, theelectrical resistivity of the formations is measured and aself-contained recorder (not shown) in the formationlogging instrument Irecords the measured resistivity values as the apparatus is traversedalong the well bore. The record of resistivity so produced isillustrated in the right-hand curve 13 of FIG. 2A.

Next, as seen in FIG. 1C, the apparatus is stopped at the predetermineddepth just above the zone being investigated, and the packer P isexpanded to isolate the section of earth formations below upperpermeable formation A from the well bore 10 above the packer P. Thestring being removed strips strips of pipe 14 is then manipulatedrelative to the set packer P to open a valve (not shown) in the flowtester F. Opening of this valve permits fluids to flow (as indicated byarrows 15) from within the permeable formations through the perforatedpipe R and on into the string of pipe 14. The tester valve is left openfor a suflicientlylong time period for the filtrate to flow out of theformations and to ensure that formation fluids have entered the stringof pipe 14.

Following the flowing operation, as seen in FIG. 1D, the packer P isreleased and the apparatus T again lowered and raised, as describedbefore. During this second upward movement, the formation resistivity isagain measured. Since this step immediately follows the flowingoperation and the well has not yet restabilized, this second loggingoperation is conducted before either a new mudcake has formed orfiltrate has reinvaded the formations. Thus, as shown by the right-handcurve 15 of FIG. 2B, a second record of resistivity is obtained in amanner similar to that described heretofore.

Following this second logging operation, the apparatus T is retrieved,as shown in FiG. 1E, and the record or log of FIG. 2A can be correlatedwith that of FIG. 23. Each particular formation stratum along thesection investigated must, of course, be precisely located in order thatlogging data from the two logging operations can be correctlycorrelated.

One manner in which this correlation can be done is to touch bottom (asshown by dashed lines in FIGS. 18 and 1D) with the test apparatus T andthen measure the travel required to bring the apparatus to the top ofthe zone being investigated. By conducting the log ging operations at aknown rate of travel, and by starting each operation from a known point,each stratum can be accurately located since the recorder chart moves ata known constant rate.

This illustrative manner of locating the particular formation strataassumes, of course, that only a single logging instrument is being usedin the testing apparatus. It is preferable, however, to include agamma-ray logging instrument with the apparatus to measure the naturalradioactivity of earth formations and to record these detectedmeasurements simultaneously with the resistivity measurements. Typicalgamma-ray logs are shown in the left-hand curves 17, 13 respectively, ofFIGS. 2A and 23. Natural radioactivity is more predominent in shale thanin other types of formations and the gamma-ray logs consequently clearlydelineate the shale formations at A from the non-shale formations at Band C. Since the level of natural radioactivity is relatively unaffectedby the flowin operation, correlation of the resistivity logs is easilyand positively accomplished.

Regardless of how the particular strata are correlated to depth, thelogging data of FIG. 2A may be correlated with that of FIG. 28 either bytransposing one log onto the other, by super-imposing one log over theother, or by simply comparing measured values. In any event, a typicalcorrelation by combining the logs of FIGS. 2A and 2B is illustrated inFIG. 2C which permits the formation interval to be evaluated as follows:

(1) Formations A maintain the same resistivity and are clearlydelineated by a high level of natural radioactivity (curves 1'7, 18) andrelatively low resistivity (curves 13, 16). Thus, formations A are shalebecause shale is known to have a high level of natural radioactivity, alow resistivity and, being impermeable, is unaffected by drilling mud.

(2) Formations B show a substantial increase in resistivity followingthe drillstern test (curve 15) over the resistivity measured before thedrillstem test (curve 13). Radioactivity is relatively low. Thus,formations B are permeable and fluid-bearing since the flowing operationhad a marked influence on the resistivity of these formations. Thenatural fluids within these formations are most likely hydrocarbonssince hydrocarbons are known to 6 have a high resistivity and theflowing operation has caused an increase in resistivity indicatingdisplacement of the mud filtrate by a higher resistivity fluid.

(3) Formations C show a significant decrease in resistivity followingthe drillstem test which moreover is substantially lower than theresistivity of formations B. Radioactivity is relatively low. Thus, asin (2) above, these formations are also permeable and fluid-bearing. Theconnate fluids within these formations are most likely water, however,since connate water at these depths is generally saline and accordinglyhas a resistivity substantially lower than the resistivity ofhydrocarbons. In the present example, it is assumed that the drillingmud chosen for use in the well is relatively fresh and that the mudfiltrate has a resistivity at least slightly higher than that of theconnate formation water. Thus, the flowing operation produced a decreasein resistivity from that of the first series of measurements, indicatingdisplacement of mud filtrate by formation water.

Other comparisons could be made with other types of formations by usingknown properties or characteristics of such formations. For example,impermeable formations other than shale would show no change inresistivity but would have only a low level of radioactivity. It is alsolikely that gaseous hydrocarbons would show a higher resistivity thanliquid hydrocarbons.

There are, of course, certain variations possible in practicing theinvention which nevertheless fall within its spirit and scope. Forexample, although the present invention is primarily concerned withconducting logging operations only along the particular formationinterval being investigated, it would be feasible nevertheless to usethe testing apparatus to log the entire span of the well bore as testingapparatus T is either being lowered in or retrieved from the well bore,or both, in addition to logging the particular zone of investigation.These instruments could, of course, he radioactivity or sonic logginginstruments as well as electrical logging instruments.

Furthermore, it is not necessary to the invention, that the loggingoperations be performed in any particular manner or limited to anyparticular number. Also, although it is preferable, it is not essentialthat any logging operation be made with testing apparatus T prior to thedrillstem-testing operation, for it may be preferred that formation logspreviously made with electric cable instruments in the conventionalmanner be substituted for the logging operations made with the apparatusof the present invention prior to the flowing operation since, in eithercase, the well would be stabilized.

The foregoing discussion has been directed to obtaining a first seriesof logging data before the flowing operation to measure the formationproperties in their stabilized condition while affected by an invasionof drilling fluid and then, after the flowing operation, obtaining asecond series of logging data before the conditions have resta'bilized.Although this sequence will permit the complete operation to beconducted in the minimum amount of time, it should be realized that thesequence could be reversed to obtain the same data as well as additionaldata.

This reversed sequence would entail performing the flowing operationinitially and then, before the well has restabilized, obtaining thefirst series of logging data. The apparatus would be held in positionuntil the well had restabilized and then the second series of loggingdata would be obtained to measure the change in properties as affectedby the invasion of drilling fluid. If desired, several series of loggingoperations could also be performed at spaced time intervals as the wellwas stabilizing to obtain useful data which would be indicative of therelative speed at which reinvasion occurred in the various strata.

The preferred manner of practicing the invention is to use a gamma-raylogging instrument in cooperation with a resistivity-measuringinstrument. Among other things,

this makes it unnecessary to measure depth. It is also preferable tostart the operation of the aforementioned instruments and the recorderby a downhole switch. In this connection, a switch coupled to the lowerend of the tool is operated by contact with the bottom of the well boreor with an obstruction therein such as a bridge plug previously setbelow the formation zone to be investigated. The switch could also beoperated by rotary motion or by signals from the surface. As it isclearly desirable to avoid running electrical conductors, such signalsfrom the surface could be in the form of acoustical impulses to triggera frequency-responsive downhole switch. Moreover, it will be appreciatedthat the formation-logging instrument could be any of the presentlyknowndevices which measure characteristics of earth formations in dependenceupon the character of the fluid content such as a chloride-ion loggingdevice.

As illustrated in FIG. 3, in the preferred embodiment of the apparatus,the flow tester may be any type of drillstem tester 19, such as thoseshown and described in either the B. P. Nutter Patent No. 2,901,001 orthe N. K. Andrew Patent No. 3,051,245. The packer 20 on the drillstemtester 19 may be a conventional expandingtype packer element made ofrubber or rubber-like material. The packer is arranged so that whenexpanded, it will sealingly engage the walls of the borehole to isolatean interval along the well bore below the packer from the hydrostaticpressure of the mud column above the packer.

Dependently secured below packer 20 is a conventional perforated anchorpipe 21 having a plurality of lateral ports 22 arranged to permit wellfluids to flow therein and on into drillstem tester 19 by way ofinternal bore 23.

Anchor pipe 21 is threadedly connected at 24 to swivel joint 25 which isarranged to rotate freely on bearings 26 and 27. Swivel joint 25 isprovided to minimize or eliminate rotation of the tester relative toformationlogging instrument 28 while drill pipe 14 is manipulated toseat and unseat packer 20 and to actuate the valve in the drillstemtester 19.

Dependently secured by threads 29 to tail piece 30 of swivel joint 25 isformation-logging instrument 28 on which is secured pad assembly 31 andswitch assembly 32. Formation-logging instrument 28 includes an outerhousing 33, preferably of metal, which encloses batteries 34, datarecorder 35, and any one or more of conventional logging instrumentssuch as, for example, gamma-ray logging instrument 36 andelectricalresistivity measuring circuits 37 in separate compartments.These logging instruments and circuits 36, 37, each detect particularproperties characteristic of the formations proximate to logginginstrument 28 and convert these results into electrical signalsrepresentative thereof. These electrical signals are then recorded ondata recorder 35, which may be any conventional type of film, tape,wire, etc., machine normally used .in the art. If housing 33 is metal,the exterior may be coated with an electrical-insulating material, suchas epoxy resin or some similar compound, to prevent the metal body fromshort-circuiting electrical current during resistivity measurements.Typical resistivity logging apparatus which can be employed is shown inU.S. Patent No. 2,669,688, an unfocused system, or the focused systemshown in U.S. Patent No. 2,712,629. Typical gamma-ray logging apparatusis shown in U.S. Patent No. 2,349,225.

Pad assembly 31 includes an insulated wall-engaging pad 38 attached tohousing 33 by a strong bowed spring 39 which is also coated with anelectrical-insulating material. Pad 38 is attached approximately at themidpoint of spring 39. Embedded in the wall-engaging face of the pad 38is a plurality of spaced-apart button-type electrodes 40. Electrodes 40are nearly flush with the wallengaging face of pad 38 or may be slightlyrecessed.

At the lowermost extremity of log ing instrument 28, switching assembly32 is arranged so that electrical power may be turned on as desired tosupply power to the various components within logging instrument 2S.Switching assembly 32 includes a relay assembly 41 which may be aconventionally-arranged holding circuit, as shown in FIG. 5, formaintaining power to the components after momentary initiation ofswitching assembly 32. If desired, the relay assembly 41 could be theone disclosed in a co-pending application, Serial No. 328,072 filedDecember 4, 1963, by Fred Pehoushek and assigned to Schlumberger WellSurveying Corporation, which permits selective turning-01f of theinstruments as well as selective turning-on of the instruments.

Relay assembly 41 is compartmentized to protect the components therein.Initiation of relay assembly 41 is accomplished by actuating contactmember 42 to momentarily close switch 43. In the particular embodimentshown in FIG. 4A, switch 43 includes two or more resilient electricalcontacts 44 spaced apart from one another in such a manner that maleconductor 45 will bridge the gap between the contacts 44 whenevercontact member 42 moves upwardly. Contacts 44 and male conductor 45 areinsulated from the housing 33 by means of insulators 46, 47,respectively. Male conductor 45 and insulator 47 are centrally locatedon top of an enlarged portion 48 of cylindrical plunger member 49 whichis received in bore 59 of switch assembly 32 and centrally located ontop of contact member 42. The annulus between bore 50 and cylindricalplunger 49 is sealed by means of O-rings 51. Compression spring 52encircles plunger 49 and is held between the upper face 53 of contactmember 42 and the lower side of shoulder 54 of spring recess 55 therebybiasing contact member 42 downwardly until enlarged portion 48 ofplunger member 49 rests on the upper side of shoulder 54.

Bottom contact member 42 also serves to release pad assembly 31 from itsretracted position in recess 56 in housing 33 upon the initial contactof contact member 42 with the bottom of borehole 10. Although it is notnecessary, it is preferred that pad assembly 31 be retracted for itsprotection when the testing apparatus is first lowered into borehole 10.

The outer ends of bowed spring 39 are fixedly attached to hinge members57, 58 which slide freely on hinge pins 59, 60 loosely received in pairsof longitudinal slots 61, 62 cut in opposite sides and at both ends ofrecess 56. In the retracted position of pad assembly 31, as partiallyshown in FIG. 4A, lower hinge member 58 is held at the bottom of slots62 to housing 33 by a shear pin 63 which is sufficiently strong toconstrain bowed spring 39 in its extended position as shown. Actuatingor thrust rod 64 is received in longitudinal bore 65 which extendsthrough the outer portion of housing 33 from the lower end of recess 56to the exposed lower end of switching assembly 32. The upper end ofthrust rod 64 contacts the under side of lower hinge member 58 whileresting freely on upper face 53 of bottom contact member 42. Thus, itwill be appreciated that when it is desired to engage pad 38 with theside of borehole 10, bottom contact member 42 is engaged with the bottomof borehole 10 or with an obstruction, such as a bridge plug. When thecombined weight of drill pipe 14 and the testing apparatus is appliedagainst this obstruction, bottom contact member 42 is thrust upwardlyagainst spring 52 to move thrust rod 64 upwardly and snap shear pin 63.Failure of shear pin 63 frees lower hinge member 58 and permits it tomove upwardly in slots 62 toward upper hinge member 57 as spring 39 bowsoutwardly into its extended position, as illustrated in FIG. 3.

In FIG. 43, an alternate embodiment 32' of switching assembly 32 isshown. Switching assembly 32' is similar to switching assembly 32 exceptthat bottom contact member 42 is a fiat plate pivoted at 66 to the lowerend of switching assembly 32. Momentary-contact switch 43' is arrangedso that actuator 67 is moved inwardly when 9 engaged by cammed surface68 on thrust rod 64 as it and contact member 4-2 move upwardly.

Other switching means can, of course, be arranged. For example, switch43 of FIG. 4A could be replaced with a momentary-contact switch such as43 of FIG. 4B.

The relay assembly 41, as illustrated in FIG. 5, will maintain powerfrom batteries 34 to recorder 35, gammaray logging instrument 35 andresistivity-measuring circuits 37 after the initial engagement ofcontact member 42 with the bottom of the borehole. The relay assemblyincludes a starting relay 69 and a holding relay 7%), both of which areconventional double-pole double-throw relays. Conductors 71 from switch43 connect the coil of relay 69 with the power supply or batteries 34carried within the instrument whenever switch 43 is closed to energizerelay 69. Relay switch 63A closes and completes a path between the powersupply 3 and the coil of relay 70, which energizes that relay. RelaysWitCh 7iiA thereby closes to complete another path from the powersupply 34 to the coil of relay 70. Relay switch 708 also closes at thesame time which would complete a path from the power supply toelectrical circuitry 35, 36 and 37 if it were not for the fact thatrelay switch 69B is now open since relay 69 is still energized. It willbe appreciated, therefore, that as soon as relay switch 698 closes inresponse to the opening of switch 43 and subsequent de-energizing ofrelay 69, a complete path will be made from power supply 34 throughrelay switch 70B and relay switch 693 to electrical circuitry 35, 3e,and 37.

While the foregoing disclosure has illustrated the apparatus asoperating in a well bore which has a relatively stable and well-packedbottom, the bottom of a well bore is often filled for several feet withcuttings, loose debris, etc., which may not be sufiiciently consolidatedto sustain the large forces required to set the packer element of adrillstem tester. When such forces are applied to set the packer, thebottom of the tool maybe driven through the bottom of the hole and forseveral feet into the earth formations with the result that the packermay be finally set an appreciable distance below the top of theformation zone being investigated. Heretofore, an operator had noaccurate indication of the amount of such displacement nor whether thepacker had been set where it would not block production from permeablestrata uppermost within the formation interval being in estigated.

Using apparatus of the present invention, however, it will beappreciated that when logs are made before and after the flowingoperation, the effect of such displacement of the tool upon setting ofthe packer will be evi denced by a longitudinal shift between the logs.Since the distance between the packing element and logging instrument isfixed by the tool configuration, the precise point where the packer wasset can be readily determined by correlating the first and second seriesof radioactivity logs to determine the amount of displacement of thetool relative to the bottom of the well bore.

An alternate variation in practicing the invention involves including abore-diameter measuring or calipering operation in conjunction with theradioactivity logging operation and, if desired, the resistivity loggingoperation.

As previously described, the flushing action during the flowingoperation will displace most, if not all, of the mud caked along theexposed faces of the fluid-bearing permeable formations within theisolated zone. Thus, it is within the scope of the present invention toobtain logs of the borehole diameters in addition to the othermeasurements previously discussed in detail. Accordingly, it will beappreciated that one series of diameter measurements will vary from theother series only by the thickness of the mudcake deposited along thepermeable zones and that such a change in the measured diameter will beobtained only along those fluid-bearing permeable strata from whichfluids were produced during the flowing operation.

It will be understood that combination of calipering or measuring withonly the radioactivity logging will merely indicate whether a particularstrata is a permeable formation capable of producing a connate fluidwhich might be either water or hydrocarbon. Thus, it is preferred tocombine the calipering operation with both the radioactivity andresistivity logging operations. A series of three logging curves will beobtained for each of the logging runs and accordingly present a moredetailed picture of changes in the formations as a result of the flowingoperation.

A typical set of logging curves is sequentially presented in FIG. 6,with FIG. 6A illustrating the logging data obtained when the well isstabilized, FIG. 6B depicting the logging data obtained immediatelyafter the flowing operation and before the well has stabilized, and FIG.60 showing the curves of FIGS. 6A and 6B superimposed or combined forcorrelation. Although FIG. 60 shows a marked variation along curveportion 71 between the diameter-measuring logs represented by curves 72and 73 of FIGS. 7A and 7B, respectively, it will be noted thatresistivity curves 74, 75 fail to exhibit any appreciable variationalong curve portion 71. It will be appreciated that in the absence ofthe diameter-measuring logs, it would probably be assumed that theparticular strata associated with curve portion 71 were eitherimpermeable or at best non-producing since there was little or no changein resistivity. The appreciable differences between the calipering logcurves 72, 73, however, quite clearly indicate that there most likely isa producing permeable formation at this point since the changes indiameter are most likely attributable to the flushing away of a mudcake.

It will be understood by those skilled in the art that such instances oflittle or no change in resistivity of a fluid-bearing permeableformation could occur, for example, whenever the resistivity of the mudfiltrate was substantially equal to that of the connate formation water.Thus, although connate formation water had displaced mud filtrate fromthe invaded zone during the flowing operation, the resistivity of theformation would exhibit little or no change. The addition of acalipering log will accordingly assist in the detection of suchconditions and eliminate the possibility that a permeable fluid-bearingformation has been overlooked FIG. 7 schematically shows an assembly ofinstruments and apparatus which would serve to obtain the caliperinglogs discussed above. The apparatus of FIG. 3 has been incorporated witha conventional calipering device 76 which could be patterned, forexample, after the apparatus disclosed in Patents No. 2,102,080 and2,267,110, for example. Calipering device 76 preferably includes threesymmetrically-arranged independent feeler arms 77 with each havingeither an outwardly-disposed pad member at its outer end or beingcurved, as at 78, to permit the tool to be raised and lowered in thewell bore. The upper end of each arm 77 is pivoted, as at 79, andprovided with a semi-circular gear segment 80. Each gear segment drivesa downwardly biased reciprocable plunger 81 having rack teeth on itslower end in engagement with the gear 80. The plungers 81 projectupwardly from the gears 80, through a sealing member, such as O-ring 82,into a sealed chamber 83. Rack teeth on the upper end of each plunger 81are drivingly engaged with a potentiometer 84 which is arranged to varyin resistance in accordance with the movement of feeler arm 77.Potentiometers 84 are incorporated in a standard bridge circuit (notshown) and connected to recorder 35 in the well-known manner. Ifdesired, the feeler arms 77 could be left free as the tool was loweredin the well bore, but it is preferred to releasably hold them againstthe side of the tool until the pad assembly 31 is released. A thrust rod(not shown) similar to the thrust rod used to release pad assembly 31 orsome similar releasing arrangement as shown in Patent No. 2,102,080could be employed to release feeler arms 77 when contact member 42 isfirst engaged with the bottom of the borehole.

A further aspect of the present invention is seen in FIG. 8 where acasing 85 has been cemented, as at 86, in place in an open well bore 87in the usual manner. Following this, a tool 88 including a radioactivitydetecting and measuring device 89 and a conventional perforatingapparatus 94} equipped with casing-collar locator 91 is lowered into thecasing on a wireline 92. This tool is lowered to the bottom of the wellto obtain a radioactivity log of the formations similar to that shown at17 in FIG. 2A in addition to a conventional log of the location of thecasing collars 93, 94. The log obtained with this radioactivity device89 is correlatable to the radioactivity logs 17, 18 obtained before thecasing was set and, therefore, the position of the collars 93, 94, aswell as the particular location of the perforating apparatus 90 in thecased well, relative to the formations is easily determined. Byutilizing such correlation, the tool 88 may be accurately positionedadjacent the collar 93 nearest to the formation of interest where theperforations are to be made. Then, using this collar 93 as a referencepoint, the perforating tool may be accurately positioned adjacent theformations of interest and operated in the well-known manner to produceperforations 95, 96 through the casing 85 into the formations.

It has heretofore been common practice to correlate formation logsobtained by conventional wireline logging instruments to the particularnumber of joints of drill pipe required to position a well tool adjacenta particular formation by calculating the amount of elongation orstretch of both the logging instruments suspension cable and that of theassembled drill string. This practice involves first calculating theamount of stretch of the suspension cable to determine the depth of aparticular formation and then calculating the amount of stretch of thedrill string supporting a well tool to determine the number of joints ofdrill pipe required to position the tool adjacent that formation. Thoseskilled in the art realize, however, that such determinations can besubject to appreciable errors particularly when the formation ofinterest is several thousands of feet below the surface.

Using apparatus of the present invention, however, it will beappreciated that formations can be located and the required number ofdrill string joints can be easily and precisely determined to enablewell tools to be accurately positioned relative to any particularformation in subsequent operations. Inasmuch as the apparatus of thepresent invention is suspended from a drill string, it will beunderstood that but for the inconsequential differences in weightsbetween the testing apparatus and subsequentlyused well tools, the drillstring will be stretched the same amount during the testing operationsas during all subsequent operations at the same depth. Thus, bycorrelating the relative location of particular zones along the span ofthe well bore to the number of joints in the drill string at the timethe testing apparatus is adjacent each particular zone, it will beunderstood that whenever it is subsequently desired to position a welltool adjacent a particular formation, all that is necessary is to lowerthat tool on a string consisting of the same number of joints of drillpipe.

Such correlation can be easily made by logging the entire span of thewell bore as the testing apparatus is either lowered into the well boreor removed therefrom. Since the logging recorder is runningcontinuously, each time the drill string is halted to allow coupling oruncoupling of another joint, the recorder will produce a substantiallyunvarying record during the interval that the drill string ismotionless. Accordingly, the logging records will consist of a series ofvarying logging measurements alternately interposed by a series ofunvarying measurements indicative of each stop of the drill string asanother joint is coupled or uncoupled. In subsequent operations,therefore, it will be necessary only to determine the actual number ofjoints in the string when the logging apparatus was adjacent anyparticular interval of formations, lower the well tool until that numberof joints has been added to the string, and then position the well toolin accordance with the location of the formation relative to the pointwhere the drill string had been halted to couple or uncouple a jointduring the testing operations. As a further aid in determining theprecise points on the logs when the drill string was halted, it ispreferred to maintain a written time record of the operations; and sincethe recorder charts have a known time base, it is but a simple matter toverify each stopping point representation on the log by determining theparticular times various chart readings were obtained.

The methods of the present invention require only that the pressure inthe well bore be reduced below the natural formation pressure of theformation interval to be tested so that the connate formation fluidswill flow into the borehole and drive the invaded filtrate out of theformation interval. Then, while only the connate fluids are in theformation interval, measurements are taken of formation properties whichare altered or affected by the presence or absence of the filtrateinvasion.

It will be appreciated, therefore, that there are several ways in whichthese steps can be performed. For example, a packer could be constructedand arranged to sealingly receive a drill string which could bereciprocated through a sleeve in the packer after it was positioned andset. The formation-logging instruments would be dependently attached tothe drill string and a valve provided in the drill string. Afterpositioning and setting the packer, the logging instruments would thenbe traversed along the full zone of investigation to obtain the firstseries of measurements. Then, the drill string valve would be opened toreduce the borehole pressure below the packer to allow the formationfluids to push the filtrate invasion out of the formation. The valvewould be left open long enough to ensure that only the connate formationfluids remained in the formations. Then, after closing the valve andwithout releasing the packer, the logging instruments would be againtraversed along the full formation interval to obtain the second seriesof measurements While the formation interval was still isolated. Hereagain, as previously described, it would not be necessary to perform theinitial logging operations before reducing the pressure in the wellbore. Other apparatus could also be used to perform the steps of thepresent invention.

It will be appreciated, therefore, that the apparatus previouslydescribed in detail is one that may also be used in the practice of themethods of the present invention. In using the apparatus illustrated inFIG. 3, the testing apparatus is lowered into well bore 10 (FIG. 1A) toa formation interval or zone to be investigated until bottom contactmember 42 engages the bottom of borehole 10 (FIG. 1B). The combinedweight of the testing apparatus and drill pipe 14 then forces bottomcontact member 42 upwardly against the force of spring 52 which closesswitch 43 thereby actuating relay assembly 41 to supply power frombatteries 34 to data recorder 35, gamma-ray logging instrument 36 andresistivity-logging circuits 37. Compression of bottom member 42simultaneously releases pad assembly 31 from its retracted positionalongside logging instrument 28 thereby allowing the pad 38 to engagethe surface of borehole 10.

As seen in FIG. 1B, the testing apparatus is then pulled upwardly at adesired rate of speed to obtain a first series of logging datacharacteristic of the formations along the formation zone beinginvestigated. The switch 43 opens when the testing apparatus is raisedbut relays 41 maintain a circuit between batteries 34 and theinstruments circuitry.

Upon reaching the upper limit of the formation interval being tested,the testing apparatus either may be halted and drillstem testingcommenced or it may again be lowered to obtain additional series oflogging data.

i3 After a desired number of series of logging operations have beenerformed, the testing apparatus is positioned and packer 20 expanded toisolate the well bore above the packer from the formation zone beinginvestigated beneath the packer.

As seen in FIG. 1C, drillstem or flow testing is conducted in theconventional manner by manipulating drill pipe 14 to open and close thevalve (not shown) contained Within drillstem tester 19 so that anyflowable fluids present in formations B, C below packer 20 will flowinto ports 22 of perforated anchor 21 and be conducted via internal bore23 upwardly through the drillstem tester and on into drill pipe 1 Assoon as the drillstem test has been completed, packer 20 is unseated tofree the testing apparatus and the apparatus is again lowered to thebottom of the borehole 1t) and then raised to obtain a second series oflogging data as shown in FIG. 1D.

Here again, if so desired, although it is not necessary the testingapparatus may traverse the formation zone being investigated as manytimes as desired if additional series of logging data are wanted.

Whenever a sufiicient number of logging operations has been conducted,the testing apparatus is then raised out of borehole 10 as seen in FIG.1E and recorder removed to permit recovery of the logs therein.

It will be appreciated from the foregoing that the present inventionprovides both novel methods and apparatus for practice of these methodsto provide data which, when correlated and studied, will permit thoseskilled in the art to make reasonable predictions as to which particularstrata of a particular formation interval investigated most likely areoil-bearing. These novel methods and apparatus permit such data to beobtained in a single operation without the necessity of making multipleround trips into and out of the well bore thereby saving considerableexpense and downtime.

The novel methods may be practiced by the novel combination of variousformation-logging instruments with a drillstem tester. Thus, a firstseries of formation logs can be taken along a particular formationfollowed by a drillstem test to drive filtrate out of the formations.The drillstem test is then immediately followed by one or moreadditional formation logs which will reflect changes in formationproperties which are altered by the presence or absence of fiitrateinvasion. Comparison of these logs will afford a significant aid in theinterpretation and evaluation of all of the logging data.

While particular embodiments of the present invention have been shownand described, it is apparent that changes and modifications may be madewithout departing rom this invention in its broader aspects and,therefore, the aim in the appended claims is to cover all such changesand modifications as fall within the true spirit and scope of thisinvention.

What is claimed is:

l. A method for investigating subterranean permeable earth formationsadjacent to a well bore containing fluids at a first pressure which haveinvaded the formations to displace natural formation fluids at a secondlower pressure therein away from the well bore, comprising the steps of:reducing the pressure in the well bore adjacent to the formations to apressure lower than the second pressure to produce invaded fluids andnatural formation fluids from those of the formations that can beproduced; and measuring a property or characteristic of the formationsaffected by the presence of produced fluids therein to determine whetherthe fluids adjacent to the well bore in any of the formations aresubstantially natural formation fluids.

2. A method for investigating an interval of subterranean permeableformations adjacent to a well bore containing fluids at a first pressurewhich have invaded the formation interval to displace natural formationfluids at a second lower pressure therein away from the well bore,comprising the steps of: isolating the portion of the well bore adjacentto the formation interval from the fluids in the remainder of the Wellbore; reducing the pressure in the isolated well bore portion to apressure lower than the second pressure to produce invaded fluids andnatural formation fluids from those formations in the isolated intervalthat can be produced; and measuring a property or characteristic of theformation interval affected by the presence of produced fluids thereinto determine whether the fluids adjacent to the well bore in any of theformations in the interval are substantially natural formation fluids.

3. In a borehole containing a mudcake-forming liquid having acharacteristic different from natural formation fluids and which hasinvaded formations to be investigated and formed a mudcake on the wallof the borehole adjacent thereto, the method of: reducing the pressurein the borehole opposite the invaded formations to produce invadedfluids and natural formation fluids from those formations that can beproduced; raising the pressure in the borehole opposite the formationsbeing investi-,

gated to re-invade the formations with such liquid and again displacenatural formation fluids away from the borehole; and before anysubstantial re-invasion has occurred, measuring a property orcharacteristic of the reinvaded formations which varies as the re-entryof the liquid displaces natural formation fluids away from the borehole.

4. A method for investigation of subterranean earth formations traversedby a Well bore using a testing assembly suspended from a string of pipe,said testing assembly including a formation-logging instrument connectedto a testing device including packing-off means for isolating a portionof a well bore and valve means selectively operable between closed andopen positions for controlling fluid communication between an isolatedwell bore portion and the string of pipe, comprising the steps of:setting the packing-off means within the well bore above a section ofearth formations to be investigated for isolating the formation sectionfrom other portions of the well bore; opening the valve means forproducing invaded and natural formation fluids from produciblefluidbearing formations along the formation section into the string ofpipe; unseating the packing-off means; and before removing the testingassembly from the well bore, logging with the formation-logginginstrument along the formation section for measuring a propertycharacteristicv of the presence of fluids in earth formations beforeremoving the testing assembly from the Well bore.

5. A method for investigation of subterranean earth formations traversedby a well bore using a testing assembly suspended from a string of pipe,said testing assembly including a formation-resistivity logginginstrument connected to a testing device including packing-off means forisolating a portion of a well bore and valve means selectively operablebetween closed and open positions for controlling fluid communicationbetween an isolated well bore portion and the string of pipe, comprisingthe steps of: setting the packing-off means within the well bore above asection of earth formations to be investigated for isolating theformation section from other portions of the well bore; opening thevalve means for producing invaded and natural formation fluids fromproducible fluid-bearing formations along the formation section into thestring of pipe; unseating the packing-off means; and measuring with theformation-resistivity instrument the electrical resistivity of theformation section for providing electrical signals representative of theelectrical resistivity and recording the electrical signals so providedas a function of the depth of the testing assembly within the well borebefore raising the testing assembly above the formation section.

6. A method for investigating subterranean permeable earth formationsadjacent to a well bore containing fluids at a first higher pressurewhich have invaded the formations to displace natural formation fluidsat a second lower pressure therein away from the well bore, comprisingthe steps of: reducing the pressure in the well bore adjacent to theformations to a pressure lower than the second pressure to produceinvaded fluids and natural formation fluids from those of the formationsthat can be produced; measuring a property or characteristic of theformations affected by the presence of fluids therein before anysubstantial re-invasion of the fluids in the well bore is expected tore-occur; and after the fluids in the well bore are expected to havere-invaded the earth formations to again displace the natural formationfluids away from the well bore, remeasuring said property orcharacteristic of the formations to obtain differences between themeasured and remeasured property or characteristic for determiningwhether natural formations fluids are produced from any of theformations when the pressure in the well bore was reduced.

7. A method for investigating an interval of subterranean permeableearth formations adjacent to a well bore containing fluids at a firsthigher pressure which have invaded the formation interval to displacenatural formation fluids at a second lower pressure therein away fromthe well bore, comprising the steps of: isolating the portion of thewell bore adjacent to the formation interval from communication with thefluids in the remainder of the well bore; reducing the pressure in theisolated well bore portion to a pressure lower than the second pressureto produce invaded fluids and natural formation fluids from thoseformations in the isolated interval that can be produced;re-establishing communication with the fluids in the remainder of thewell bore to restore the pressure of the fluids in the well boreadjacent to the formation interval to the first pressure; measuring aproperty or characteristic of the formation interval affected by thepresence of fluids therein before any substantial re-invasion of thefluids in the well bore is expected to re-occur; and after the fluids inthe well bore are expected to have re-invaded the formation interval toagain displace the natural formation fluids away from the well bore,remeasuring said property or characteristic of the formation interval toobtain differences between the measured and remeasured property orcharacteristic for determining whether natural formation fluids wereproduced from any of the formations in the interval when the pressure inthe isolated well bore portion was reduced.

8. In a bore-hole containing a mudcake-forming liquid having acharacteristic different from natural formation fluids and which hasinvaded earth formations to be investigated to form a mudcake on thewall of the borehole adjacent thereto, the method of: reducing thepressure in the borehole opposite the formations to be investigated toproduce invaded fluids and natural formation fluids from those of theformations that can be produced; raising the pressure in the boreholeopposite the formations being investigated to re-invade the producibleformations with such liquid and again displace natural formation fluidstherein away from the borehole; and before any substantial re-invasionis expected to have occurred, measuring a property or characteristic ofthe formations being investigated which varies as the entrance of theliquid again displaces natural formation fluids in any re-invadedformations away from the borehole; and after a substantial re-invasionis expected to have occurred, remeasuring said property orcharacteristic of the formations to obtain differences between saidmeasured and remeasured property or characteristic for determiningwhether natural formation fluids were produced from any of theformations being investigated when the pressure in the borehole wasreduced.

9. A method for investigation of subterranean earth formations invadedby fluids from within a well bore with a testing assembly suspended froma string of .pipe and including a formation-logging instrument,packing-off means for isolating a portion of a well bore and valve meansselectively operable between closed and open positions for controllingfluid communication between an isolated well bore portion and the stringof pipe, comprising the steps of: setting the packing-off means withinthe well bore above a section of earth formations to be investigated forisolating the formation section from other portions of the well bore;opening the valve means for producing invaded and natural formationfluids from producible fiuidbearing formations within the formationsection into the string of pipe; unseating the packing-off means; beforeany substantial re-invasion of fluids is expected to have occurred,logging with the formationlogging instrument the formation section formeasuring a property characteristic of the presence of fluids in earthformations; and then, after a substantial re-invasion of the produciblefluid-bearing formations is expected to have occurred, relogging withthe formation-logging instrument the formation section for remeasuringsuch property before removing the testing assembly from the well bore.

10. A method for investigating subterranean permeable earth formationsadjacent to a well bore containing fluids at a first higher pressurewhich have invaded the formations to displace natural formation fluidsat a second lower pressure therein away from the well bore, comprisingthe steps of: measuring a property or characteristic of the formationsaffected by the presence of fluids therein; reducing the pressure in thewell bore adjacent to the formations to a pressure lower than the secondpressure to produce invaded fluids and natural formation fluids fromthose of the formations that can be produced; and remeasuring saidproperty or characteristic of the formations before any substantialre-invasion of the fluids is expected to re-occur to obtain differencesbetween said measured and remeasured property or characteristic fordetermining whether natural formation fluids were produced from any ofthe formations when the pressure in the well bore was reduced.

11. A method for investigating an interval of subterranean permeableearth formations adjacent to a well bore containing fluids at a firsthigher pressure which have invaded the formation interval to displacenatural formation fluids at a second lower pressure therein away fromthe well bore, comprising the steps of: measuring a property orcharacteristic of the formation interval affected by the presence offluids therein; isolating the portion of the well bore adjacent to theformation interval from communication with the fluids in the remainderof the well bore; reducing the pressure in the isolated well boreportion to a pressure lower than the second pressure to produce invadedfluids and natural formation fluids from those formations in theisolated formation interval that can be produced; re-establishedcommunication with the fluids in the remainder of the well bore torestore the pressure of the fluids in the Well bore adjacent to theformation interval to the first pressure; and before any substantialre-invasion of the fluids in the well bore into the producibleformations in the interval is expected to re-occur and again displacethe natural formation fluids away from the well bore, remeasuring saidproperty or characteristic of the formation interval to obtaindifferences between said measured and remeasured property orcharacteristic for determining whether natural formation fluids wereproduced from any of the formations in the interval when the pressure inthe isolated well bore portion was reduced.

12. A method for investigation of subterranean earth formations invadedby fluids from within a well bore with a testing assembly suspended froma string of pipe and including a formation-logging instrument,packing-off means for isolating a portion of a well bore, and valvemeans selectively operable between closed and open positions forcontrolling fluid communication between an isolated well bore portionand the string of pipe, comprising the steps of: logging with theformation-logging instrument a section of earth formations to beinvestigated for measuring a property characteristic of the presence offluids in earth formations; setting the packing-off means above theformation section being investigated for isolating the formation sectionfrom other portions of the well bore; opening the valve means forproducing invaded and natural formation fluids from produciblefluid-bearing formations within the formation section into the string ofpipe; unseating the packing-off means; and before any substantialre-invasion of fluids into the producible formations is expected tooccur, relogging with the formation-logging instrument the formationsection for remeasuring such property.

13. A method for investigation of subterranean earth formations invadedby fluids Within a well bore with a testing assembly suspended from astring of pipe and including a formation-resistivity measuringinstrument, packing-off means for isolating a portion of a well bore,and valve means selectively operable between closed and open positionsfor controlling fluid communication between an isolated well boreportion and the string of pipe, comprising the steps of: measuring withthe formationresistivity instrument the electrical resistivity of asection of earth formations to be investigated for providing a firstseries of electrical signals representative of the measured electricalresistivity and recording the first series of electrical signals soprovided as a function of the depth of the instrument within the wellbore; setting the packing-off means above the formation section beinginvestigated for isolating the formation section from other portions ofthe well bore; opening the valve means for producing invaded and naturalformation fluids from producible fluid-bearing formations within theformation section into the string of pipe; unseating the packing-offmeans; and, before any substantial re-invasion of fluids is expected tohave re-occurred, remeasuring with the formation-resistivity instrumentthe electrical resistivity of the formation section for providing asecond series of electrical signals representative of the remeasuredelectrical resistivity and recording the second series of electricalsignals so provided as a function of the depth of the testing assemblywithin the well bore before raising the testing assembly above theformation section.

14. The method of claim 13 further including the step of: correlatingthe first series of recorded signals with the second series of recordedsignals to measure any differences therebetween for determining whethernatural formation fluids were produced from any of the formations in theformation section when the valve means Was opened.

15. A method for investigation of subterranean earth formations invadedby fluids within a well bore with a testing assembly suspended from astring of pipe and including a formation-resistivity measuringinstrument, a radioactivity-measuring instrument, packing-off means forisolating a portion of a well bore, and valve means selectively operablebetween closed and open positions for controlling fluid communicationbetween an isolated well bore portion and the string of pipe, comprisingthe steps of: measuring with the formation-resistivity andradioactivity-measuring instruments the electrical resistivity andradioactivity of a section of earth formations to be investigated forproviding a first and second series of electrical signals respectivelyrepresentative of the measured electrical resistivity and radioactivityand recording the first and second series of electrical signals soprovided; setting the packing-off means above the formation sectionbeing investigated for isolating the formation section from otherportions of the well bore; opening the valve means for producing invadedand natural formation fluids from producible fluid-bearing formationswithin the formation section into the string of pipe; unseating thepacking-01f means; and, before any substantial reinvasion of fluids isexpected to have re-occurred, remeasuring with the formation-resistivityand radioactivitymeasuring instruments the electrical resistivity andradioactivity of the formation section for providing a third and fourthseries of electrical signals respectively representative of theremeasured electrical resistivity and radioactivity and recording thethird and fourth series of electrical signals so provided before raisingthe testing assembly above the formation section.

16. A method for determining the location of a packer seat in an openwell bore comprising the steps of: moving a string of tools suspendedfrom a string of pipe and including a drillstem tester, a packer, and alogging device coupled to one another with the logging device beingspaced at a known distance relative to the packer into a well bore, and,while moving the string of tools upwardly from the bottom of the wellbore to a predetermined depth thereabove, recording as a function ofdistance from the bottom of the well bore a first series of measurementsof at least one characteristic of the earth formations; lowering thelower end of the string of tools to the bottom of the well bore forsetting the packer at a predetermined position in the well bore belowsaid predetermined depth; operating the drillstem tester; unsetting thepacker; again moving the string of tools upwardly to above thepredetermined position and recording as a function of distance from thebottom of the well bore a second series of measurements of said onecharacteristic of the earth formations; and thereafter measuring thedifference in indicated depths of reproduced measurements on the firstand second log records to determine the actual distance from the bottomof the Well bore to the point where the packer was set.

17. A method for completing wells comprising the steps of: passing intoan open Well bore on a drill string a first tool including a firstradioactivity logging device and a tester with a packer means and aselectively-operable valve; logging with said first radioactivitylogging device the earth formations traversed iby the well bore toobtain a first log; testing at least some of the earth formations loggedwith the logging device by isolating a section of the well bore with thepacker means and flowing fluids into the drill string by operating thetester valve; and subsequently, after casing of the well bore, passing asecond tool into the cased well bore including a perforating means and asecond radioactivity logging device; logging with said secondradioactivity device the earth formations traversed by the casing toobtain a second log; and then positioning said perforating meansadjacent such earth formations to be completed as determined bycorrelation of said first and second logs to one another; and thereafteroperating said perforating apparatus.

18. A method for completing wells comprising the steps of: passing intoan open well "bore on a drill string a first tool including a firstradioactivity logging device and a tester with a packer means and aselectively-opera ble "valve; logging with said first radioactivitylogging device the earth formations traversed by the well bore to obtaina first log; testing at least some of the earth formations logged withthe logging device by isolating a section of the well bore with thepacker means and flowing fluids into the drill string by operating thetester valve; and subsequently after casing of the well bore, passing asecond tool into the cased well bore including a perforating means, acasing collar locator and a second radioactivity logging device; loggingwith said second radioactivity device the earth formations traversed bythe casing to obtain a second log; and then positioning said perforatingmeans at earth formations to be completed as determined by correlationof said first and second logs to one another and the location of acollar adjacent to the earth formations to be completed; and thereafteroperating said perforating apparatus.

19. The method of positioning a well tool suspended from a string ofseparable sections of pipe at a selected depth in a well bore adjacent aparticular earth formation traversed by the well bore comprising thesteps of: positioning apparatus including a logging instrument at theend of a string of separable sections of pipe at a first depth in thewell bore; traversing the apparatus and pipe string in a particulardirection along the well bore from said first depth to a second depthwhile operating the logging instrument to obtain varying representationscharacteristic of at least one property of the different earthformations adjacent to the Well bore between said first and seconddepths; halting the apparatus and pipe string at said second depth tovary the length of the pipe string by coupling or uncoupling a separablesection of pipe and to obtain substantially unvarying representationscharacteristic of said one property of the particular formation adjacentto the logging instrument at said second depth; alternately halting andtraversing the apparatus and pipe string at successive depths in thesame particular direction until the apparatus has reached a third depthin the well bore whereby the logging instrument provides a loggingrecord having a first successive series of said varying representationsfor each traversal along the well bore of the apparatus alternating witha second successive series of unvarying representations for each haltingof the apparatus in the well bore; removing the apparatus and pipestring; positioning a well tool on the pipe string at one of said firstand third depths; and then positioning the well tool at a selected depthintermediate of said third and first depths by coupling or uncoupling toor from the pipe string a number of said separable pipe sectionscorresponding to removing the apparatus and pipe string; positioning awell tool on the pipe string at one of said first and third depths; thenumber of said unvarying representations on the logging record betweensaid third depth and said selected depth.

20. The method of positioning a well tool suspended from a string ofseparable sections of pipe at a selected depth in a well bore adjacent aparticular earth formation traversed by the well bore comprising thesteps of: positioning apparatus including a radioactivity sensingandrecording instrument at the end of a string of separable sections ofpipe at a first depth in the well bore; traversing the apparatus andpipe string in a particular direction along the well bore from saiddepth to a second depth while operating said radioactivity instrument toobtain of varying measurements or radioactivity levels of the differentearth formations adjacent the well bore between said first and seconddepths; halting the pipe string at said second depth to vary the lengthof the pipe string by coupling or uncoupling a separable section of pipeand to obtain a second series of substantially unvarying measurements ofthe radioactivity level of the particular formation adjacent theradioactivity instrument at said second depth; alternately halting andtraversing the apparatus and pipe string at successive depths in thesame particular direction until the apparatus has reached a third depthin the well bore whereby the radioactivity instrument provides a loggingrecord having a first successive series of said varying measurements foreach traversal along the well bore of the apparatus alternating withsaid second successive series of unvarying measurements for each haltingof the apparatus in the well bore; removing the apparatus and pipestring; positioning a well tool on the pipe string at one of said firstand third depths; and subsequently positioning the well tool at aselected depth intermediate of said third and first depths by couplingor uncoupling to or from the pipe string a number of said separable pipesections corresponding to the number of said unvarying measurements onthe logging record between said third depth and said selected depth.

21. The method of determining the particular number of separablesections of pipe required to assemble a pipe string of suflicient lengthto position a well tool at a selected depth in a well there relative toa datum point at the surface of the ground comprising the steps of:positioning a logging instrument at the end of a string of separablesections of pipe at a first depth lower than said selected depth;retrieving said string while logging and successively stopping saidstring whenever a separable section reaches said datum point to obtain alogging record characteristic of at least one property of the earthformations adjacent said well bore from said first depth to at least asecond depth above said selected depth, said logging record beingperiodically interrupted by successive substantially unvaryingrepresentations corresponding to the formations adjacent each positionwhere said instrument was successively stopped; then determining fromsaid successive unvarying representations on said logging record theparticular number of separable sections in the pipe string whenever saidlogging instrument passed said selected depth; and subsequentlysuspending a well tool on a string of pipe consisting of that particularnumber of separable sections to position said well tool at said selecteddepth.

22. The method of positioning a well tool suspended from a string ofpipe at a particular depth including the steps of: lowering from a datumpoint at the earths surface an apparatus including a logging instrumentin a string of pipe to a given depth in a well bore where said string ofpipe is comprised of separable sections and said logging instrument willprovide a log of earth formations while moving with said string of pipeand distinctive indications whenever the string of pipe is halted touncouple such sections of pipe at the earths surface; retrieving saidapparatus while said logging instrument is operating by successivelyuncoupling such sections of pipe at the earths surface; and thenpositioning a well tool at a particular depth in the well bore relativeto said given depth by reassembling a string of pipe comprising a numberof said separable sections corresponding to the number of saiddistinctive indications between said datum point and said particulardepth as determined from said log.

23. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having packer means forpacking-off between said device and the periphery of the well bore forisolating a portion of the well bore from the rest of the well bore,said flow-controlling device including a fluid passage through saidpack-ofl means for communicating an isolated well bore portion with adrill pipe, and valve means for selectively controlling fluidcommunication through said passage; and a formation-logging instrumentcoupled to said flow-controlling device and having means for detecting aproperty characteristic of the presence of fluids within earthformations for determining the effect of fluid production from earthformations.

24. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having packer means forpacking-0E between said device and the periphery of the well bore forisolating a portion of the well bore from the rest of the well bore,said flow-controlling device including a fluid passage through saidpack-off means for communicating an isolated well bore portion with adrill pipe, and valve means for selectively controlling fluidcommunication through said passage; a formation-logging instrumentcoupled to said flow-controlling device and having electrical sensingmeans for detecting a property characteristic of the presence of fluidswithin earth formations; and power source means connected to saidelectrical means.

25. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having packer means forpacking-off between said device and the periphery of the well bore forisolating a portion of the well bore from the rest of the well bore,said flow-controlling device including a fluid passage through saidpack-off means for communicating an isolated Well bore portion with adrill pipe, and valve means for selectively controlling fluidcommunication through said passage; and a formation-logging instrumentcoupled to said flow-controlling device and having electrical means forsensing a detectable property characteristic of the presence of fluidswithin earth formations and providing an electrical signalrepresentative of such detected property, recording means forregistering such electrical signals, and power source means connected tosaid electrical sensing means, said sensing means, recording means andpower source means being completely contained in said formation-logginginstrument.

26. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having packer means packing-01fbetween said device and the periphery of the well bore for isolating aportion of the well bore from the rest of the well bore, saidflow-controlling device including a fluid passage through said pack-01fmeans for communicating an isolated well bore portion with a drill pipe,and valve means for selectively controlling fluid communication throughsaid passage; a formation-logging instrument coupled to saidflow-controlling device and having first electrical sensing means fordetecting a property characteristic of the presence of fluids withinearth formations, and second electrical sensing means for detecting theemission of radioactive gamma rays from earth formations; and powersource means connected to said first and second electrical sensingmeans.

27. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having acker means for packingolfbetween said device and the periphery of the well bore for isolating aportion of the well bore from the rest of the well bore, saidflow-controlling device including a fluid passage through said pack-offmeans for communicating an isolated well bore portion with a drill pipe,and valve means for selectively controlling fluid communication throughsaid passage; a formation-logging instrument coupled to saidflow-controlling device and having first electrical means for sensing adetectable property characteristic of the presence of fluids withinearth formations and providing a first series of electrical signalsrepresentative of such detected property, second electrical means forsensing the emission of radioactive gamma rays from earth formations andproviding a second series of electrical signals representative of suchradioactivity, recording means for separately registering such series ofelectrical signals, and power source means; and switching means forselectively connecting said power source means to said electrical means.

28. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having packer means forpacking-off between said device and the periphery of the well bore forisolating a portion of the well bore from the rest of the well bore,said flow-controlling device including a fluid passage through saidpack-off means for communicating an isolated Well bore portion with adrill pipe, and valve means for selectively controlling fluidcommunication through said passage; a formation-logging instrumentcoupled to said flow-controlling device and having electrical means forsensing electrical resistivity of earth formations; and a downhole,self-contained power source means connected to said electrical means.

29. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having packer means forpacking-off between said device and the periphery of the well bore forisolating a portion of the well bore from the rest of the well bore,said flow-controlling device including a fluid passage through saidpack-off means for communicating an isolated well bore portion with adrill pipe, and valve means for selectively controlling fluidcommunication through said passage; and a formation-logging instrumentcoupled to said flow-controlling device and having electrical means forsensing electrical resistivity of earth formations and providing aseries of electrical signals representative of such electricalresistivity, recording means for registering such series of electricalsignals, and power source means connected to said electrical means, saidsensing means, recording means and power source means being completelycontained in said formation-logging instrument.

30. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having packer means forpacking-off between said device and the periphery of the well bore forisolating a portion of the well bore from the rest of the well bore,said flow-controlling device including a fluid passage through saidpack-oft" means for communicating an isolated well bore portion with adrill pipe, and valve means for selectively controlling fluidcommunication through said passage; and a formation-logging instrumentcoupled to said flow-controlling device and having first electricalmeans for sensing electrical resistivity of earth formations, secondelectrical means for detecting the emission of radioactive gamma raysfrom earth formations, and power source means connected to saidelectrical means.

31. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having packer means forpackingoif between said device and the periphery of the well bore forisolating a portion of the well bore from the rest of the well bore,said flow-controlling device including a fluid passage through saidpack-off means for communicating an isolated well bore portion with adrill pipe, and valve means for selectively controlling fluidcommunication through said passage; a formation-logging instrumentcoupled to said flow-controlling device and having first electricalmeans for sensing electrical resistivity of earth formation andproviding a first series of electrical signals representative of suchelectrical resistivity, second electrical means for sensing the emissionof radioactive gamma rays from earth formations and providing a secondseries of electrical signals representative of such radioactivity,recording means for separately registering such series of electricalsignals, and power source means; and switching means for electricallyconnecting said power source means to said electrical means in responseto engagement of said switching means with a surface of a well bore.

32. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of dr'l pipe and having packer means forpacking-ofl between said device and the periphery of the well bore forisolating a portion of the well bore from the rest of the well bore,said flow-controlling device including a fluid passage through saidpack-off means for communicating an isolated well bore portion with adrill pipe, and valve means for selectively controlling fluidcommunication through said passage; and a formationlogging instrumentcoupled to said flow-controlling device and having electrical means forsensing electrical resistivity of earth formations.

33. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having packer means forpackingolf between said device and the periphery of the well bore forisolating a portion of the well bore from the rest of the well bore,said flow-controlling device including a fluid passage through saidpack-off means for communicating an isolated well bore portion with adrill pipe, and valve means for selectively controlling fluidcommunication through said passage; and a formation-logging instrumentcoupled to said flow-controlling device and having first electricalmeans for sensing a detectable property characteristic of the presenceof fluids within earth formations and providing a first series ofelectrical signals representative of such detected property, secondelectrical means for sensing the emission of radioactive gamma rays fromearth formations and providing a second series of electrical signalsrepresentative of such radioactivity, recording means for concurrentlyregistering each of such series of electrical signals, power sourcemeans, and switching means for electrically connecting said power sourcemeans to said first and second electrical means upon engagement of saidswitching means with a surface of a well bore.

34. Apparatus adapted for passage through a well bore for evaluatingfluid-production capabilities of subterranean earth formations traversedby the well bore comprised of: a flow-controlling device adapted forcoupling to a string of drill pipe and having packer means forpackingoff between said device and the periphery of the well bore forisolating a portion of the well bore from the rest of the well bore,said flow-controlling device including a fluid passage through saidpack-off means for communicating an isolated well bore portion with a.drill pipe, and valve means for selectively controlling fluidcommunication through said passage; and a formation-logging instrumentcoupled to said flow-controlling device and having first electricalmeans for sensing electrical resistivity of earth formations andproviding a first series of electrical signals representative of suchelectrical resistivity, second electrical means for sensing the emissionof radioactive gamma rays from earth formation and providing a secondseries of electrical signals representative of such radioactivity,recording means for concurrently registering each of such series ofelectrical signals, power source means, and switching means forelectrically connecting said power source means to said first and secondelectrical means upon engagement of said switching means with a surfaceof a well bore.

References Cited by the Examiner UNITED STATES PATENTS 2,156,052 4/1939Cooper 73152 X 2,320,863 6/1943 Green 200-6142 X 2,320,890 6/1943Russell 166-4 2,459,499 1/ 1949 Castel ZOO-61.42 X 2,320,890 6/1943Russell 166-4 2,650,067 8/ 1953 Martin 73-152 X 3,038,333 6/1962 Allenet al. 73-155 RICHARD C. QUEISSER, Primary Examiner. I. W. MYRACLE,Assistant Examiner.

17. A METHOD FOR COMPLETING WELLS COMPRISING THE STEPS OF: PASSING INTOAN OPEN WELL BORE ON A DRILL STRING A FIRST TOOL INCLUDING A FIRSTRADIOACTIVITY LOGGING DEVICE AND A TESTER WITH A PACKER MEANS AND ASELECTIVELY-OPERABLE VALVE; LOGGING WITH SAID FIRST RADIOACTIVITYLOGGING DEVICE THE EARTH FORMATIONS TRAVERSED BY THE WELL BORE TO OBTAINA FIRST LOG; TESTING AT LEAST SOME OF THE EARTH FORMATIONS LOGGED WITHTHE LOGGING DEVICE BY ISOLATING A SECTION OF THE WELL BORE WITH THEPACKER MEANS AND FLOWING FLUIDS INTO THE DRILL STRING BY OPERATING THETESTER VALVE; AND SUBSEQUENTLY, AFTER CASING OF THE WELL BORE, PASSING ASECOND TOOL INTO THE CASED WELL BORE INCLUDING A PERFORATING MEANS AND ASECOND RADIOACTIVITY LOGGING DEVICE; LOGGING WITH SAID SECONDRADIOACTIVITY DEVICE THE EARTH FORMATIONS TRAVERSED BY THE CASING TOOBTAIN A SECOND LOG; AND THEN POSITIONING SAID PERFORATING MEANSADJACENT SUCH EARTH FORMATIONS TO BE COMPLETED AS DETERMINED BYCORRELATION OF SAID FIRST AND SECOND LOGS TO ONE ANOTHER; AND THEREAFTEROPERATING SAID PERFORATING APPARATUS.